The invention relates generally to power-driven modular plastic conveyor belts and, more particularly, to modular plastic conveyor belts hingedly interconnected row to row by pairs of hinge pins.
Conventional modular conveyor belts and chains are constructed of modular links, or belt modules, arranged in rows. Spaced apart hinge eyes extending from each end of the modules include aligned openings. The hinge eyes along one end of a row of modules are interleaved with the hinge eyes of an adjacent row. A single pivot rod, or hinge pin, journalled in the aligned openings of end-to-end connected rows, connects adjacent rows together to form an endless conveyor belt capable of articulating about a drive sprocket or drum.
Because they do not corrode and are easy to clean, modular plastic conveyor belts are often used instead of metal belts. Usually, the hinge pins in plastic belts are also made of plastic. The hinge pins are typically circular in cross section and reside in circular openings in the hinge eyes. Relative rubbing motion, known as scrubbing, between the hinge pins and the walls of the hinge eyes as the belt articulates about sprockets tends to wear both the hinge pin and the hinge eye wall. This wear tends to wallow out the openings in the hinge eyes and increase the pitch of the belt. In abrasive environments, such as in conveying potatoes and other agricultural products, this wear is accelerated by the intrusion of dirt and grit into the hinges of the belt.
Metal hinge pins are sometimes used to increase the wear life of the pins. But that does not do away with the relative motion between pin and hinge eye wall, and belt module wear at the hinge is still a problem.
Non-circular hinge strips made of a flexible material have been proposed to resist wear. Hinge eyes forming slots with flared ends permit the confined hinge strip to flex a limited angle without frictionally rubbing with the hinge eyes as the belt articulates. Such an arrangement is effective in increasing wear life, but the flexible hinge strip is inherently weak in shear strength and unsuitable for carrying heavy loads.
Some power transmission chains constructed of metal components use a pair of pins in each joint between consecutive groups of links. At each joint, one pin is wedged into the openings of one group of links and another pin, in rocking engagement with the first pin, is wedged in the openings of the adjacent group of links. In this way, relative motion is confined to the rocking surfaces of the metal pins. But transmission chains and modular conveyor belts operate in different environments and serve different purposes. Power transmission chains often are used in well-lubricated environments, relatively free of abrasives, as in internal combustion engines and other machinery in which the use of gears is impractical. Modular conveyor belts, on the other hand, are frequently used in very abrasive, non-lubricated environments to move various products over long distances.
Thus, there is a need for a modular plastic conveyor belt that can resist wear at the hinge for a long operating life even in abrasive environments.
This need and others are satisfied by a modular plastic belt having features of the invention. The belt is formed of a series of rows of belt modules having a conveying surface. Each row includes one or more belt modules extending from a forward end to a rearward end in the direction of belt travel. A first set of hinge eyes is arranged along the forward end, and a second set of hinge eyes is arranged along the rearward end. Aligned openings are formed in the hinge eyes. The rows are arranged end-to-end with the first set of hinge eyes of a row interleaved with the second set of hinge eyes of an adjacent row. The rows are hingedly connected together to form a conveyor belt by a plurality of hinge pin pairs, each of which includes a first hinge pin and a second hinge pin. Each hinge pin further has an outer contact surface. The first and second hinge pins of each pair are arranged side by side in the aligned openings in the interleaved hinge eyes at the ends of each row to connect consecutive rows into a conveyor belt with a hinge between consecutive rows.
In preferred versions of the conveyor belt, the hinge pins are circular in cross-section, preferably of the same diameter, or oval with the same contact surface radius. This reduces the number of unique parts and helps prevent scrubbing.
In other versions, the openings flare out from a narrow end to a wide end and form, for example, a triangular-shaped opening with a vertex at the narrow end and a base at the opposite wide end. In another variation, the openings resemble bicycle seats. The first hinge pins reside in the narrow ends of the openings in the hinge eyes along the forward end of the row, and the second hinge pins reside in the wide ends of the openings in the hinge eyes along the forward end of the row. The narrow end of the opening in the hinge eye forms a constraining portion of the opening to maintain the position of the hinge pin relative to the belt module. The wide end of the opening is bounded by a roll surface along which the hinge pin rolls as the belt articulates. Preferably, the narrow end is the proximal end of the opening and the wide end is the distal end of the opening in the hinge eye. As the belt bends and the rows rotate relative to each other, the outer contact surfaces of the first and second hinge pins roll against each other and along the roll surfaces of the hinge-eye openings instead of rubbing against the hinge eye.
Thus, a conveyor belt embodying features of the invention eliminates relative rubbing contact between hinge pin and belt module, thereby making such a conveyor belt particularly long-lasting in abrasive environments.